This article describes preschool social understanding and difficult behavior (hot temper, disobedience, bossiness and bullying) as predictors of Oppositional Defiant Disorder (ODD) and Aggressive Conduct Disorder (ACD) in a Dutch population sample of (pre)adolescents (N = 1943), measured at age 10-12 and at age 13-15. ODD and ACD were assessed by the Child Behavior Checklist and the Youth Self-Report, preschool behavior was evaluated by the parental questionnaire ‘How was your child as a preschooler? (age 4-5)’. Adjusted for each other, all difficult preschool behaviors except bullying were associated with adolescent ODD, while only bullying significantly predicted adolescent ACD. Furthermore, the results suggest a qualitative difference between ODD and ACD in terms of the social component of the disorders: poor preschool social understanding was associated with the development of ACD but not of ODD; and poor social understanding interacted with difficult preschool behaviors to predict later ACD but not ODD. No major differences were found between boys and girls, nor did we find strong evidence for differences between preadolescent (age 10-12) and early adolescent (age 13-15) outcomes. The finding that poor social understanding was implicated in the developed of ACD but not in the development of ODD may help to demarcate the individuality of each disorder and offer leads for (differential) treatment strategies.